The present invention relates to a radio wave shield.
Recently, radio wave equipment such as in-house PHS and radio LAN is being rapidly prevailing. In accordance with the prevalence, it has become indispensable to adjust the radio wave environment within an office for preventing information leakage and preventing malfunction or noise caused by externally intruding radio waves. Therefore, various techniques for adjusting the radio wave environment have been proposed (see, for example, Japanese Patent Publication No. 6-99972 and Japanese Laid-Open Patent Publication No. 10-169039).
Japanese Patent Publication No. 6-99972 discloses a technique to construct a skeleton of a building by using concrete including an electromagnetic shielding material made of an electromagnetic wave reflector or an electromagnetic wave absorber. However, the electromagnetic shielding material described in Japanese Patent Publication No. 6-99972 does not have frequency selectivity. In other words, this electromagnetic shielding material shields incident radio waves regardless of their frequencies. Therefore, in the technique described in Japanese Patent Publication No. 6-99972, a radio wave of a specific frequency cannot be selectively shielded but radio waves of frequencies not to be shielded are shielded.
On the other hand, Japanese Laid-Open Patent Publication No. 10-169039 discloses a technique to secure an electromagnetic shielded space within a building by forming an electromagnetic shielding plane by periodically arranging Y-shaped linear antennas. It is described that a radio wave of a necessary frequency alone can be electromagnetically shielded by this technique.
Most of conventional radio wave equipment have used radio waves of one or more specific frequencies (with a fractional bandwidth of 10% or less). However, radio wave equipment using radio waves of a specific frequency band with a given width (such as a cellular phone) has been recently proposed. Accordingly, there are increasing needs for a radio wave shield for adjusting the radio wave environment in an office or a building where such radio wave equipment using a specific frequency band (such as radio wave equipment using radio waves with a fractional bandwidth larger than 10%) is utilized.
The technique described in Japanese Laid-Open Patent Publication No. 10-169039 is, however, used for shielding a radio wave of a specific frequency, and hence, it is difficult to employ this technique to adjust the radio wave environment in an office or the like where the radio wave equipment using radio waves of a specific frequency band is utilized.
The present invention was devised to overcome such a conventional problem, and an object of the invention is providing a radio wave shield usable for adjusting the radio wave environment in an office or the like where the radio wave equipment using radio waves of a specific frequency band is utilized.